Spinal stenosis is a condition or disease causing narrowing of the spinal canal and compression of the spinal nerves. Spinal stenosis affects millions of people world wide and leads to symptoms of back and leg pain, weakness, numbness and trouble walking Spinal stenosis is a particularly common problem among older individuals and can result in severe disability and lack of normal mobility. Spinal stenosis is one of the most common conditions requiring spinal surgery. Surgery for spinal stenosis is required to alleviate compression of the spinal nerves and improve the symptoms of back and leg pain, weakness, numbness and trouble walking.
The traditional surgical operation for spinal stenosis is a called a laminectomy. This procedure involves cutting away the spinal lamina or posterior bony covering of the spinal canal, followed by trimming of the medial portions of the facet joints to expand the room available to the spinal nerves. Some surgeons prefer to use similar procedure called a laminotomy which removes only a portion of the spinal lamina followed by trimming of the facet joints to expand the room available for the spinal nerves.
More recently, implantable medical devices called intraspinous spacers have been used to treat spinal stenosis. These devices are designed to wedge between the spinous processes of two adjacent vertebrae, blocking the vertebral joint from extending or bending backward. Because the spinal canal becomes most narrow in the extended position, intraspinous devices can help a subset of spinal stenosis patients that only experience pain while standing.
Although laminectomy, laminotomy and intraspinous spacer devices may all be successful for patients with spinal stenosis, each of these approaches has significant limitations in a significant proportion of patients with spinal stenosis. For instance, laminectomy generally is a major spinal operation requiring general anesthesia which can lead to complications especially in older patients. Several important disadvantages have been identified with the use of laminectomy to treat spinal stenosis such as damage to back muscles, destabilization of the spine and scarring around the nerve roots. In some cases, destabilization of the spine may cause a serious forward slippage of one vertebra on the adjacent vertebra requiring a major revision surgery called spinal fusion. Also, laminectomy requires a large surgical incision, leading to the risk of major bleeding and the need for general anesthesia. Because most patients with spinal stenosis are elderly, major surgery such as laminectomy may lead to medical complications, making this approach suboptimal for the older, medically fragile patient. In addition, laminectomy may not provide a permanent cure for spinal stenosis, which recur causing the need for further major surgery in the future.
Laminotomy is quite similar to laminectomy but does not require removal of the entire bony lamina. Like laminectomy, laminotomy is normally performed under general anesthesia and involves trimming away portions of the spinal lamina and facet joints to decompress the spinal nerves. Advocates of laminotomy believe that the laminotomy approach may lessen the risks of spinal destabilization and nerve scarring compared to laminectomy. However, laminotomy still requires major open spinal surgery and general anesthesia. It also is more technically difficult to perform compared to laminectomy and may not adequately relieve the pressure on the spinal nerves. In addition, there is a risk that with time, the spinal stenosis may recur, leading to the need for additional surgery.
Recently, intraspinous process spacers, such as the device described by Zucherman, et. al. (U.S. Pat. No. 5,836,948) have been described for the treatment of spinal stenosis. These devices are designed to be wedged between the spinous processes, and block the vertebral joint from assuming an extended position. Because the extended position causes the spinal canal to be smaller, the avoidance of this position may alleviate the symptoms of spinal stenosis in a subset of patients with symptoms only while standing (or bending backward; i.e., extending) that are relieved with sitting (or bending forward; i.e., flexing). This subset of patients generally have less severe narrowing of the spinal canal and may achieve relief of pain by blocking the position of the vertebral joint leading to the worst narrowing of the spinal canal.
Unfortunately, intraspinous devices only provide a slight expansion of the spinal canal compared to laminectomy and laminotomy. Thus, intraspinous spacers are only useful in the subset of spinal stenosis patients with relatively mild stenosis. Also, because the narrowed spinal canal is not significantly enlarged, and because the narrowing of the spinal canal worsens with time, intraspinous process device may only provide temporary relief of the symptoms of spinal stenosis. Thus, many patients treated with laminectomy may ultimately require a laminectomy as their condition worsens. Also, intraspinous process spacers are not able to be used in patients whose spinous processes are weakened by osteoporosis or absent due to a prior laminectomy procedure.
For all these reasons, a better treatment approach to spinal stenosis is needed. In U.S. Pat. No. 6,358,254, issued Mar. 19, 2002, entitled “A Method and Implant for Expanding a Spinal Canal,” and in U.S. Pat. No. 7,166,107, issued Jan. 23, 2007, entitled “Percutaneous Technique and Implant for Expanding the Spinal Canal”, novel inventions are disclosed whereby the spinal canal can be expanded by cutting and lengthening the spinal pedicles. The present invention describes further, novel instruments, devices, spinal implants and methods pertaining to the art of pedicle lengthening that can be used to expand the spinal canal for the correction of spinal stenosis. The present invention provides significant advantages compared to the prior art methods and devices for treating spinal stenosis.
In U.S. patent application Ser. No. 10/386,357 (US 2003/0212400) to Bloemer et al., a method for expansion of the spinal canal is disclosed. In Bloemer, spinal stenosis is treated by cutting, distracting and holding spinal pedicles with implanted devices. However, the approach of Bloemer has certain limitations and disadvantages that severely limit its usefulness for treating spinal stenosis. First, no cutting method or tools disclosed by Bloemer allow the bone cuts to be performed. The work of the present invention has demonstrated that safe and accurate cutting of the spinal pedicles is highly complex given the dense bone of the spinal pedicles and the close proximity of the bone cuts to the delicate nerve tissue and fluid filled dural sac. In addition, the shape of the spinal pedicles is not regular but rather the bone of the pedicle forms an irregular shape in cross section that resembles an oval. In addition, the bone of the pedicle has thick and thin regions which make the cutting task a substantial challenge for which no instruments or tools have been previously known to the art of spine and bone surgery.
Second, the implants disclosed by Bloomer fail to gain purchase within the pedicle bone cut, but rather rely on bony purchase within the pedicle bore. Research surrounding the present invention has shown that due to the soft or poor quality bone within the upper region of the pedicle, an implant as disclosed by Bloemer would not gain adequate bony purchase to achieve the distraction force necessary to create a gap within the pedicle sufficient in size to expand the spinal canal.
Third, the device of Bloemer does not provide for the geometric offset that tends to occur during pedicle lengthening. Because of the lateral to medial angulation of the pedicles, there is the potential for the pedicle lengthening maneuver of the pedicles to produce a malalignment between the upper (proximal) and lower (distal) portion of the implant. This potential problem was not anticipated by Bloemer, and thus no mechanism to contend with geometric offset was disclosed by Bloemer.
Fourth, the disclosure of Bloemer provides no means to precisely align the pedicle cut with the portion of the implant that performs the pedicle lengthening maneuver. Proper alignment of the implant with the pedicle cut is crucial for the pedicle lengthening device to work correctly and yet no means to achieve this alignment was disclosed.
For all these reasons, Bloemer fails to provide a workable concept to achieve pedicle lengthening for the correction of spinal stenosis. Not surprisingly, the work of Bloemer has not been reduced to practice within the field of spine surgery, nor has research on the technique been disclosed in the public domain. Therefore, additional novel inventions are required to overcome these limitations and provide a functional means for achieving a correction of spinal stenosis through pedicle lengthening.
In view of the foregoing, a new, less invasive method to correct spinal stenosis without the limitations of current methods is needed to address the disabling symptoms suffered by millions of individuals with spinal stenosis. The optimal treatment method must be safe, reproducible, effective in eliminating nerve pressure and minimally invasive so that older patients or those with health problems could be treated without the need for major, risky surgery. The present invention achieves these goals.